1. Field of the Invention
This invention relates to a stratified burning internal combustion engine equipped with a combustion chamber and an intake port structure, which are particularly suited for stratified burning.
2. Description of the Related Art
Stratified burning internal combustion engines have been known conventionally. With a view toward permitting driving at low fuel consumption, they form a fuel-rich layer of an air-fuel mixture in a combustion chamber and ignite the fuel-rich layer so that an air-fuel mixture having a low air-fuel ratio as a whole can be ignited.
As one example of such stratified burning internal combustion engines, a stratified burning internal combustion engine in which stratified vertical tumble flows, that is, vertical vortices (hereinafter simply referred to as "tumble flows") are formed has already been commercialized as illustrated in FIGS. 37 and 38.
FIGS. 37 and 38 show the structure of one of cylinders of a 2-intake-port internal combustion. engine, in which there are illustrated a cylinder block 322, a cylinder 324, a piston 326, a cylinder head 328 and a combustion chamber 330. Designated at numeral 334 is an upper wall of the combustion chamber 330. The upper wall 334 is shaped in the form of a pentroof which has inclined walls 334a,334b. Intake ports 340,342 are open through the inclined wall 334a of the combustion chamber 330 and are each provided with an intake valve 358. Incidentally, numeral 347 indicates an exhaust port arranged in communication with an exhaust passage 360, while numeral 359 designates an exhaust valve.
Intake air, which has flowed into the combustion chamber 330 through the respective intake ports 340,342, then flows along the inclined wall 334b toward an inner wall of the cylinder 324, said inner wall being located on extensions of axes of the individual intake ports 340,342, whereby tumble flows are formed in the combustion chamber 330 as indicated by arrows Fa,Fm.
As is depicted in FIG. 37, only one of the intake ports, namely, the intake port 342 is provided with an injector 312. A spark plug 310 is arranged adjacent to the intake valve 358 in the intake port 342 which is provided with the injector 312. In the vicinity of the spark plug 310, there is accordingly formed the tumble flow Fm of an air-fuel mixture which has been formed of inducted air and fuel injected from the injector 312, so that stratified tumble flows consisting of the tumble flow Fm of the air-fuel mixture and the tumble flow Fa of air are formed in the combustion chamber 330.
Even when the ratio of the air to the fuel inside the combustion chamber 330 is high, in other words, even upon lean burn in which the fuel concentration is low as a whole inside the combustion chamber 330, stable combustion is still feasible owing to the existence of an air-fuel mixture richer in fuel than those present at places remote from the spark plug 310, around the spark plug 310.
Further enhancement of stratification inside the combustion chamber permits lean burn at a still greater air-fuel ratio. Further strengthening of tumble flows makes it possible to achieve a further enhancement of stratification.